1. Field of the Invention
The present invention is related to bubble memory devices. More particularly, the present invention is related to an improved detector device for a thick film single layer bubble memory which is arranged to detect continuous bit bubble streams.
2. Description of the Prior Art
Prior art bubble memory devices are well-known and are generally classified in U.S. Class 340, subclass 174 (International Class G11C 11/14).
Prior art thick bubble memory devices such as Model TIB0203 and TIB0303 are thick film devices manufactured by Texas Instrument Company and employ a plurality of storage loops for storing bubble domains. When the information represented by the bubble stream is to be retrieved from one of the individual storage loops, the stream is diverted or replicated through a detector array.
The voltage signal which is produced by a single bubble domain passing through a detector stage is very weak and it has become a desired practice to enlarge the bubble domain into a large elongated domain to increase the voltage response in the detector. A typical prior art chevron-shaped pattern expanding stage has been employed before entering a detector stage and such expanding stages are shown in U.S. Pat. No. 3,953,840. The detector stage in this patent is similar to the detector stage employed in the TIB0203 bubble memory device and such detectors have generally been classified as alternate bit detectors because the stream of bubbles being detected must be separated one from the other by a space or absence of a bubble domain in order to be operable. In binary logic the absence of a bubble domain is identified as a "0" bit and the presence of a bubble domain is identified as a "1" bit. Since the bubbles in a bubble stream must be spaced out or delayed to be detected in an alternate bit detector, it has been suggested that continuous bit detectors be employed in bubble memory devices.
Alternate bit detectors employ two similar detector stages side by side, accordingly, these detector stages are subject to substantially the same environment and the signal-to-noise ratio does not produce a problem in detecting the difference between the presence of a bubble domain and the absence of a bubble domain.
Consecutive bit detectors of the type employed in the present invention employ similar detector stages. However, these detector stages are separated one from the other by a substantial distance on the device. Because of this separation of the detector stages, the magnetic field environment acting on the detector stage and the dummy detector stage may be so different that the signal-to-noise ratio sensed in the detector may cause the bubble memory device to be unusable.
It has been suggested that a high signal-to-noise ratio can be achieved in a consecutive bit detector even though the dummy detector stage is substantially removed from the detector stage by creating a substantially identical field at the two stages. Since the detector stage is a very small portion of a bubble chip, it is not practical to achieve this end by creating a separate external field or a modified external field which is operable only with the dummy detector stage.
It is not economically desirable to create two complete and separate detector arrays so that the dummy detector stage and the detector stage are subject to identical environments. Further, it would not be practical to duplicate the environment of the detector stage at the dummy detector stage by providing an array which was identical to the detector stage. Either of these proposed alternatives would require too much area on a bubble chip to be a practical solution. Further, there is no assurance that the two identical separated detector stages would create substantially identical field environments since the distance the detector stages would be separated one from the other may magnify the nonuniformities of the rotating field.